Conventional guide wires for angioplasty and other vascular procedures usually comprise an elongated core member with one or more tapered sections near the distal end thereof and a flexible body such as a helical coil disposed about the distal portion of the core member. A shapeable member, which may be the distal extremity of the core member or a separate shaping ribbon which is secured to the distal extremity of the core member, extends through the flexible body and is secured to a rounded plug at the distal end of the flexible body. Torquing means are provided on the proximal end of the core member to rotate, and thereby steer, the guide wire while it is being advanced through a patient's vascular system.
In a typical PTCA procedure, a guiding catheter having a preformed distal tip is percutaneously introduced into the cardiovascular system of a patient in a conventional Seldinger technique and advanced therein until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guide wire is positioned within an inner lumen of a dilatation catheter and then both are advanced through the guiding catheter to the distal end thereof. The guide wire is first advanced out of the distal end of the guiding catheter into the patient's coronary vasculature until the distal end of the guide wire crosses a lesion to be dilated, then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient's coronary anatomy over the previously introduced guide wire until the balloon of the dilatation catheter is properly positioned across the lesion. Once in position across the lesion, the balloon is inflated to a predetermined size with radiopaque liquid at relatively high pressures (e.g., greater than 4 atmospheres) to press the arteriosclerotic plaque of the lesion against the inside of the artery wall and to otherwise expand the inner lumen of the artery. The balloon is then deflated so that blood flow is resumed through the dilated artery and the dilatation catheter can be removed therefrom.
A major requirement for guide wires is that they have sufficient column strength to be pushed through a patient's vascular system or other body lumen without kinking. However, they must also be flexible enough to avoid damaging the blood vessel or other body lumen through which they are advanced. Efforts have been made to improve both the strength and flexibility of guide wires to make them more suitable for their intended uses, but these two properties are for the most part diametrically opposed to one another in that an increase in one usually involves a decrease in the other.
Currently, x-ray fluoroscopy is the preferred imaging modality for cardiovascular interventional procedures because no other imaging method has the temporal or spatial resolution provided by fluoroscopy. However, x-ray imaging has many drawbacks for both the patient and the clinician. The iodinated contrast agents employed in x-ray fluoroscopy are nephrotoxic with a low but measurable incidence of short-term renal failure and allergic reactivity. The ionizing radiation from the x-ray fluoroscopy can be an issue for the patient during protracted or repeated interventions and is a daily issue for the interventionalist and staff who must cope with the burden of personal dose monitoring and wearing lead shielding.
The use of MRI for observing interventional procedures has been performed for balloon angioplasty and stent placement. The use of this imaging modality is quite attractive because it eliminates some of the problems inherent with x-ray imaging. On the other hand, conventional guide wires which are suitable for x-ray fluoroscopy are not suitable for use in MRI observed interventional procedures due to their magnetic attraction, large magnetic susceptibility artifact, and potential heating when exposed to RF energy.
What has been needed and heretofore unavailable is a guide wire which is safe and compatible for use in conjunction with MRI. The present invention satisfies these and other needs.